Plus Therapeutics Initiates Manufacturing Activities with SpectronRx Under a Master Services Agreement to Support GMP Pivotal Trial Readiness for REYOBIQ™

Plus Therapeutics Boosts REYOBIQ Manufacturing for Pivotal Trial Readiness

Plus Therapeutics announced the initiation of manufacturing activities and technology transfer with SpectronRx under a Master Services Agreement (MSA) to support late-stage clinical manufacturing of REYOBIQ (rhenium Re186 obisbemeda). This strategic partnership establishes SpectronRx as a second GMP manufacturing site, complementing Radiomedix, and secures Rhenium-186 isotope supply through Telix Pharmaceuticals. The collaboration significantly strengthens Plus Therapeutics' multi-partner supply chain infrastructure, bolstering manufacturing readiness and expanding production capacity as REYOBIQ advances towards pivotal trials for central nervous system (CNS) cancers, with a target milestone to complete manufacturing scale-up by 2026.

• The Master Services Agreement with SpectronRx encompasses the technology transfer of the REYOBIQ manufacturing process, Rhenium-186 isotope processing, analytical methods, and regulatory expertise. SpectronRx's Indiana facility will provide integrated, on-demand manufacturing capabilities for both Rhenium-186 isotope production and REYOBIQ drug manufacturing within the same facility, aiming to improve coordination and simplify logistics.
• This partnership is a critical step in strengthening Plus Therapeutics' multi-partner supply chain infrastructure, ensuring reliability and scalability for REYOBIQ's late-stage clinical supply needs and future commercialization. By adding SpectronRx as a second GMP site alongside Radiomedix and securing isotope supply from Telix Pharmaceuticals, the company aims to meet its 2026 target milestone for manufacturing scale-up.
• REYOBIQ (rhenium Re186 obisbemeda) is a novel injectable radiotherapy designed to deliver targeted high-dose radiation to CNS tumors, utilizing Rhenium-186 for its therapeutic beta energy and real-time imaging gamma energy. It is currently being evaluated in the ReSPECT-GBM, ReSPECT-LM, and ReSPECT-PBC clinical trials for recurrent glioblastoma, leptomeningeal metastases, and pediatric brain cancer, respectively, supported by significant grants from the NCI, CPRIT, and the U.S. Department of Defense.

Addressing Critical Unmet Needs in CNS Cancers with Enhanced Supply

Recent advances in CNS oncology have highlighted persistent therapeutic challenges across three critical patient populations. Despite multimodal treatment approaches, significant unmet medical needs remain for recurrent glioblastoma, leptomeningeal metastases, and pediatric brain cancers. Current research efforts are focusing on novel therapeutic strategies and better patient stratification to address these gaps.

• Recurrent glioblastoma represents one of the most challenging oncologic scenarios, with virtually all patients experiencing relapse despite maximal safe resection, radiochemotherapy, and adjuvant temozolomide, leading to mean overall survival under 18 months

• Treatment resistance mechanisms continue to evolve during tumor progression, with molecular characteristics and genetic alterations changing over time, significantly affecting the efficacy of precision medicine approaches and contributing to therapeutic failure

• Limited therapeutic options exist once tumors progress after first-line therapy, with traditional systemic therapies including nitrosoureas and temozolomide rechallenge demonstrating only marginal efficacy in the recurrent setting

• Leptomeningeal metastases from high-grade gliomas remain an uncommon but devastating complication with poor prognosis, where patients are significantly less likely to survive beyond one year compared to those with brain metastases only

• Intrathecal chemotherapy optimization represents a critical unmet need for leptomeningeal disease, with inconsistent dosing regimens and frequencies reported across studies, and additional research warranted to maximize therapeutic efficacy

• Pediatric brain cancers continue as the leading cause of cancer deaths in children, with treatment-resistant tumors harboring unique genetic aberrations and aggressive phenotypes conferring particularly poor prognoses despite recent therapeutic advances

• Preclinical model limitations hinder the development of novel pediatric brain cancer therapeutics, with conventional models failing to accurately represent the molecular heterogeneity and immune microenvironment observed in clinical scenarios

• Patient stratification challenges persist across all three populations, with 76% of recurrent glioblastoma studies lacking molecular criteria in study design, limiting the translation of targeted therapies to genome-driven clinical trials

Rhenium-186 Obisbemeda: A Targeted Radiotherapy with Broad Potential

The mechanism of action underlying rhenium-186 obisbemeda is being explored across several cancer types beyond its primary neurological indications. In head and neck squamous cell carcinoma, a Phase I dose-escalation study evaluated 186Re-labeled chimeric monoclonal antibody U36 in 13 patients with recurrent or metastatic disease. The trial established a maximum tolerated dose of 27 mCi/m2, with myelotoxicity identified as the dose-limiting factor. Clinical efficacy was demonstrated with marked tumor size reduction in two patients and stable disease maintained for six months in another patient.

The radioimmunotherapy approach is being investigated in hematological malignancies, particularly B-cell lymphomas and multiple myeloma. For malignant lymphoma, radiolabeled antibodies targeting CD20-positive cells have shown substantial complete remission rates in chemotherapy-resistant cases, with trials exploring both myeloablative regimens with stem-cell transplant support and nonmyeloablative protocols as initial therapy for low-grade disease. In multiple myeloma, CD38-targeted radioimmunotherapy is advancing through preclinical models and clinical trials, leveraging the uniformly high expression of this glycoprotein on myeloma cells.

Additional applications span solid tumor types including non-small-cell lung cancer, where iodine-labeled cadonilimab (a PD-1/CTLA-4 bispecific antibody) has demonstrated tumor-targeting retention and enhanced CD8+ T cell infiltration. Liver tumors represent another target, utilizing yttrium-90-labeled particles for both primary and secondary hepatic malignancies. Across these indications, locoregional administration routes are showing particular promise for achieving superior tumor-to-normal tissue ratios, especially in low tumor burden settings, though bone marrow suppression remains the primary dose-limiting toxicity even with regional delivery approaches.

Navigating the Current Treatment Landscape for CNS Cancers

Current standard of care treatments for CNS cancers vary significantly across disease types, with established protocols for some conditions while others remain areas of active investigation. The treatment landscape continues to evolve with emerging therapies showing promise in early studies, though many require further validation in larger clinical trials.

• Recurrent glioblastoma can be treated with re-irradiation using active scanning proton therapy, which preserves health-related quality of life until disease progression, or MR-guided adaptive radiotherapy using 1.5 Tesla MR-Linac with manageable acute toxicities

• Leptomeningeal metastases management follows EANO-ESMO Clinical Practice Guidelines (2022) with conventional treatments including chemotherapy, photon-based radiation therapy, and intrathecal chemotherapy, though novel approaches like molecularly targeted therapies, antibody-drug conjugates, and proton craniospinal irradiation show promise

• Pediatric glioblastoma standard care involves multimodal treatment with surgery, radiotherapy, and temozolomide chemotherapy, though outcomes remain poor with median survival of 14.6 months and high treatment resistance due to glioma stem cell populations

• Pediatric brain tumors generally are managed with surgery, radiation therapy, chemotherapy and immunotherapy combinations, though optimal treatment protocols remain undefined and aggressive therapy often leads to long-term sequelae in survivors

• Infantile glioblastoma (≤1 year) shows distinct treatment patterns with 86% receiving surgery, 59% chemotherapy, and 20% radiation therapy, achieving notably better median overall survival of 67.3 months compared to other age groups

• Experimental therapies under investigation include [177Lu]Lu-PSMA therapy for progressive glioblastoma, CDK4/6 inhibitors, oncolytic virotherapy, CAR-T cell therapies, and Tumor Treating Fields technology, though clinical efficacy requires confirmation in larger studies

A Strategic Leap for Rhenium-186 in Brain Cancer

The recent announcement by Plus Therapeutics regarding the expansion of REYOBIQ's manufacturing capabilities marks a significant milestone in the development of this novel radiopharmaceutical for central nervous system (CNS) cancers. By establishing SpectronRx as a second GMP manufacturing site and securing Rhenium-186 isotope supply through Telix Pharmaceuticals, the company is proactively addressing one of the most critical challenges in radiopharmaceutical development: a robust and resilient supply chain.

This move is not merely about increasing capacity; it's about de-risking the entire late-stage clinical program and future commercialization. Radiopharmaceuticals, by their very nature, have unique logistical hurdles due to the short half-lives of their isotopes and specialized production requirements. A multi-partner supply chain mitigates potential disruptions, ensuring consistent availability for pivotal trials and, ultimately, for patients battling aggressive CNS malignancies where treatment options are often limited.

However, the path forward is not without its complexities. Research indicates that Rhenium-186, while a viable beta-emitter for brain tumors, exhibits a lower dose rate compared to agents like Yttrium-90 or Phosphorus-32 for the same concentration in intracranial cysts. This inherent characteristic necessitates meticulous optimization of dosing strategies and administered activity levels during clinical development to ensure therapeutic efficacy while managing potential safety profiles. The successful technology transfer and scale-up across multiple sites by 2026 will be crucial, demanding stringent quality control and process validation. As REYOBIQ advances, its ability to demonstrate clear clinical differentiation and a favorable risk-benefit profile against existing or emerging therapies will be paramount for its eventual market success in this challenging oncology landscape. This strategic manufacturing expansion sets the stage, but the clinical data will ultimately define its impact.